That deal was agreed on Friday night, meaning that the 19-year-old was available for selection by manager Stuart Malcolm the day after to bolster a squad hit by suspensions and injuries against Scottish Lowland Football League leaders Bonnyrigg Rose.
Dundee-born Dow joined the Fifers in September 2020, making six appearances for their first team.
Prior to that, he was on Dundee United’s books at youth level, also spending time at Scottish Junior Football Association East Region Midlands League side Carnoustie Panmure on loan before and since.
Dow took injured Graham Taylor’s place in Saturday’s starting line-up in Midlothian but wasn’t able to get his career with the Northumbrians off to a winning start as their hosts put three unanswered goals past them at New Dundas Park.
Rangers kept Rose at bay for the opening half-hour of Saturday’s game, but Ross Gray, Callum Connolly and Kerr Young then managed to find ways through their visitors’ defences.
Gray opened the scoring by getting a touch to the ball during a goalmouth tussle on 31 minutes, Connolly doubled the hosts’ lead on 57 minutes with a composed finish and Young made sure of all three points on 70 minutes by volleying home.
That was a second defeat on the trot for Berwick after going down 1-0 at home to Bo’ness United in midweek, but they’ll be looking to bounce back during their upcoming break from league duties.
First up is a trip to West Calder United in the East of Scotland Cup this Saturday at 2.30pm.
That’s followed by another cup game at home to league rivals Gretna 2008 on Monday, September 20.
That Scottish Cup first-round tie, kicking off at 7.45pm, is being screened live by BBC Scotland on Monday, September 20, and club chairman Brian Porteous said: “We’re delighted that the BBC cameras will be coming down to Shielfield Park and it’s fantastic news for us as a club, and it will also bring some excellent exposure for our dedicated sponsors.”